For application in BEM/FMM shielding calculations a simple analytical model for the loading noise of contra rotating open rotors (CRORs) with different rotational speeds is derived. Following previous work of S.L.A. Glegg, the model is formulated in frequency domain and the pressure is approximated by a set of dipoles on circles on the propeller disk. The dipole strength depends on the blade loading function and can be obtained, e.g., by CFD calculations. For arbitrary rotational speeds, the blade loading function is not a perodic function on the propeller disk anymore and must be approximated, e.g., by a least-squares Fourier approximation. The CROR model is checked against a time domain solution using rotating dipoles and validated with data from a test of Rolls-Royce's open rotor model rig 145 in DNW. The lowest three and most dominant peaks in the spectrum of the uninstalled rotor are well predicted by the method with errors less than 3dB with a correct directivity. For higher frequencies larger errors are observed. The CROR model has been developed for shielding calculations with the DLR BEM/FMM code. Some information about the code is given and the applicability of the model is demonstrated for a CROR installed at a modified DLR F6 aircraft geometry.